Process of producing boranes



United States Patent many, a corporation of Germany N0 Drawing. Filed Mar. 19, 1962, Ser. No. 180,814 Claims priority, appliclagion Germany, Mar. 20, 1961,

4 Claims. (a. 23-204 The present invention relates to a process of producing boranes and more particularly to a process of producing polyboranes and their substitution products.

It is known to produce diborane by reacting boron trichloride and monosilane. The reaction is carried out in the presence of methyl radicals which are obtained by photochemical decomposition of diazomethane. This process, however, is not suitable for large scale production of diborane because the explosive diazometh-ane can be handled only with difiiculty. Furthermore, considerable amounts of non-volatile compounds are formed. The yield of diborane is rather low. The diborane is also contaminated by methane which can be separated from the gas mixture only with great difficulty.

It is one object of the present invention to provide a simple and effective process of producing diborane and higher liquid boranes such as pentaborane and the like, as well as partly substituted boranes.

Other objects of the present invention and advantageous features thereof will become apparent as the description proceeds.

In principle the process according to the present invention consists in reacting inorganic silanes with boron halogenides in the presence of a catalyst capable of specifically activating the formation of boranes. Catalysts which are especially suitable for the process according to the present invention are large surface catalysts. Especially suitable has proved to be activated charcoal in the form of particles having a diameter of 1 mm. to 3 mm. It is of importancethat such large surface catalysts are as free as possible of oxygen and moisture in order to avoid side reactions. A catalyst, which is especially useful for the present reaction, can be obtained, for instance, by heating commercially available activated charcoal at a temperature between 200 C. and 400 C. in a vacuum for one hour to ten hours. When using such a catalyst in the reaction of inorganic silanes with boron halogenides, the resulting borane compounds are obtained in a high yield and are substantially free of methane.

The reaction according to the present invention proceeds, for instance, according to the following equation:

The reaction is preferably carried out under atmospheric pressure conditions. The. reaction sets in with a satisfactory speed of reaction even at room temperature. Since the reaction proceeds strongly exothermically, it is usually required to intensely cool the reaction vessel and/or to dilute the reactants by the addition of inert gases such as hydrogen, nitrogen, or noble gases such as argon. Dilution with inert liquids is also possible.

Preferably the reaction is carried out at a temperature between about 20 C. and about 150 C. Best results are achieved at a temperature between 20 C. and 50 C. When reacting at a temperature exceeding 80 0., not only diborane but also higher liquid boranes such as pentaborane are formed. An increase of the reaction temperature above 150 C. is to be avoided because the resulting borane are further decomposed thermally at such higher temperatures. The reaction temperature can 3,165,3815 Patented Jan. 12,, 1965 readily be controlled by the speed of adding the reactants and diluting agents.

The process according to the present invention is especially suitable for the production of diborane in a high yield. On passing a gas mixture of four parts by volume of boron trihalogenide and three parts by volume of monosilane over dehydrated and degasified activated charcoal at a temperature below 50 C., the gas mixture withdrawn after reaction of said reactants consists of diborane and tetrahalogeno silane, partly also of trihalogeno silane, and contains usually small amounts of halogeno boranes. To produce substantially pure diborane, the resulting diborane which may contain halogen is passed through washing vessels or scrubbers containing organo silanes such as triethyl silane. Any halogeno silane present in the reaction product is retained by said scrubbers and the residual halogeno boranes are converted into diborane which is withdrawn together with the initially present diborane. In place of organo silanes, there may be used in these scrubbers N-trialkyl borazanes such as N-triethyl borazane. It is also possible and sometimes of advantage to combine and use both organo silanes and N-trialkyl borazanes.

When varying the proportion of four parts by volume of boron trihalogenide to three parts by volume of monosilane, there are obtained, in addition to diborane, silanes containing varying amounts of halogen. Thus, for instance, when using monosilane in a considerable excess, there is formed monohalogeno silane (SiH Cl). A small excess of monosilane produces especially trihalogeno silane.

. MRX 'y In said formula M indicates boron or aluminum;

R indicates lower alkyl, lower alkoxy, or lower phenoxy;

R indicates hydrogen or halogen; x is an integer from 1 to 3, and x-l-y together amount to 3.

The resulting silanes can again be reacted with boron halogenides. Thus, the silanes may be considered as hydrogen transfer agents. It may be pointed out that direct reaction of the boron halogenide with sodium hydride under the low temperature conditions of this process is not possible.

The term inorganic silanes used in the specification and the claims annexed thereto not only comprises monosilane which is the preferred hydrogenatin g agent but also halogeno silanes such as dihalogeno silane (SiH Cl Boron halogenide compounds useful in the process according to the present invention are the boron trihalogenides preferably boron trichloride and boron tribromide. It is also possible to react a boron halogenide which contains one or two hydrogen atoms, such as monochloroborane or dichloro'borane. When using boron halogenide compounds which are partly substituted by organic radicals, i.e. boron halogenides of the formula The process according to the present invention has the wherein X is halogen; R is a lower alkyl or aryl; and n is the integer 1 or 2,.

- the corresponding substituted organo boranes are obtained. By using partly substituted boron halogenide. and the inorganicsilane in a corresponding stoichiometric proportion, quantitative reaction is assured; Y

Boranes are-useful as starting materials for the preparation'or organo-boron compounds or of metal boron.

hydride's. They may also be employed as motor fuels and as additives to motor fuels of'high energycontent.

Furthermore, boron of the highest degree or purity can Example A mixture of 93 g; of boron trichloride and 18 g. of

monosilane-are passed, Within three hours, through a tubewhich is filled with g. of degasified and dehydrated activatedcharcoal asit is sold, for instance, bythe firm E. Merck A.G. of Darmstadt, Germany. Care is taken that the exothermic reaction which sets in immediately is kept at a temperature below about C(bY external cooling. The emerging gas mixture is passed through a condenser kept at 78 C. wherein the resulting chloro silanes are condensed'and 1iquefied,-while diborane'passcs therethrough. The crude diborane obtained thereby is.

conducted through another condenser kept at 78' C., thereafter through a scrubber containing triethyl silane, and finally into triethylamine. 76 g. of N-triethyl borazane are obtained corresponding to a yield of. diborane of about 86% of the theoretical yield. The condensed chloro silane mixture consists mainly of trichloro silane (about and some dichloro silane andtetrachloro silane.

When replacing monosilane in the above given example by halogeno silanes such as dichloro silane,'and otherwise proceeding as described in the. above given example, it is also possible to produce diborane in a high yield.-

When the'temperature is increasedto70-150 C., the yield of diborane is reduced but the yield of pentaborane is increased. At a temperature of C. the yield of diborane is 30% and of pentaborane is 70% of the total amount of formed boranes. Additional admixture of hydrogen to monosilane in equivalent volumes results in a higher yield of diborane of about 90%.

same as described in said example.

Such boron boron dichloride or dimethyl' boron chloride, phenyl.

boron dichloride, diphenyl boron bromide, ethylboron dichloride,. diethyl boron chloride, and other substituted boron halogenides, reaction with monosilane yields the borane, diethyl borane, phenyl borane, diphenylborane and similar compounds. e t V Of course, many changes and variations in the proportions of boron halogenide, inorganic silanes, and diluting agents, in the reaction conditions, temperature and duration, in the processes of recovering diborane'from the reaction products and of purifying the same, and the like may be made by those skilled'in the art inaccordance with-the principles set forth herein and-inthe' claims annexed hereto.

Iclaim: I f

1. In a process of producing boranes, thesteps which comprise reacting. an inorganic silane selected from the group consisting of monosilane and halogeno monosilanes 'With'a boron halogenide of the formula rRx 'y wherein X indicates a halogen; V R indicates a member selected ing of alkyl and aryl; R"indicates a member'selected from the group consisting of hydrogen, alkyl, and aryl;v :1 indicates an integer from 1 to 3; x indicates the-integers Oto 2; I y indicates the integers 0'to 2; and n+x+y together beingthe integer. 3; I a at a temperature between about 20? C. and about C. in the presence of dehydrated activated charcoal as catalyst.

2. The process according to claim 1, wherein the activated charcoal used as catalyst is an activated charcoal which has been dried in ,a-vacuum by heatingat a temfromthe group consistperature between about 200 C. and about 400 C. for

one hour to ten hours.

3. The process accordingto claim 1, wherein the reaction temperature is a temperature between about 20 C. and about 50 C; i

4. In aprocess of producingdiborane of highest purity,

the steps which comprise reacting 'boron trichloride with mono'silane at a temperature between about 20 C. and.

about 50 C. in the presenceofdried activated charcoal as catalyst, conducting. the resulting gas. mixture through a condenser cooled to. atemperatureof about +78 C. to

a washing'liquid selectedfromthe group consisting of organo silanes and N-trialkyl borazanes.

References Cited by the Examiner UNITED' STATES. PATENTS 2,994,586 8/61 Huff 23 -204 3,007,768 11/61 Edwards et'al. 2314 I FOREIGN PATENTS 1,245,583 10/60 France. 864,253 3/ 61, Great Britain.

MAURICE A. BRINDIS I, Primary Examiner} BENJAMIN I'IENKIN,v Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,165,381 January 12, 1965 Herbert Jenkner It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 44, for "+78 6." read -78? c.

Signed and sealed this 3rd day of August 1965.

(SEAL) Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. IN A PROCESS OF PRODUCING BORNAES, THE STEPS WHICH COMPRISE REACTING AN INORGANIC SILANE SELECTED FROM THE GROUP CONSISTING OF MONOSILANE AND HALOGENO MONOSILANES WITH A BORON HALOGENIDE FO THE FORMULA 